1. Field of the Invention
The present invention relates, in general, to a liquid crystal display apparatus. More particularly, the present invention relates to a Light-Emitting Diode (LED) driving apparatus for driving a LED when it is used as a light source of a liquid crystal display apparatus, and a liquid crystal display apparatus using the same.
2. Discussion of Related Art
In general, a liquid crystal display apparatus is a display apparatus, in which a liquid crystal layer having an anisotropic dielectric constant is formed between front and rear substrates (that is, transparent insulating substrates), and molecular arrangements of a liquid crystal material are changed by controlling the intensity of an electric field formed in the liquid crystal layer. Thus, a desired image is displayed depending on the amount of light transmitting to the front plate (that is, a display surface).
The liquid crystal display apparatus is a light-receiving type display apparatus that does not emit light itself, and thus requires a backlight disposed on a rear surface of a liquid crystal panel on which an image is displayed and serving to uniformly maintain the brightness of the whole screen.
A light source of the backlight for the liquid crystal display apparatus comprises a Cold Cathode Fluorescent Lamp (CCFL), an External Electrode Fluorescent Lamp (EEFL) or the like. Recently, a LED lamp has been in the spotlight as a next-generation light source, which has an excellent energy saving effect compared with the CCFL or EEFL and can be used semi-permanently.
The LED has usually been used for the light source of a backlight for a small-sized liquid crystal display apparatus, such as mobile phones. However, as the luminance of the LED is enhanced, the utilization range of the LED gradually expands to the light source of a backlight for a large-sized liquid crystal display apparatus.
A LED for a backlight of a conventional liquid crystal display apparatus and a driving apparatus thereof will be described below.
FIG. 1 is a view illustrating a conventional LED driving apparatus.
As illustrated in FIG. 1, the driving apparatus of the LED for the backlight of the conventional liquid crystal display apparatus comprises a plurality of LEDs LED11 to LED13, LED21 to LED23, and LED31 to LED33, LED drivers 10, 20 and 30 for driving the plurality of LEDs LED11 to LED13, LED21 to LED23, and LED31 to LED33, respectively, and DC-DC converter units 12, 22 and 32 for supplying constant voltages to the plurality of LEDs LED11 to LED13, LED21 to LED23, and LED31 to LED33, respectively.
The driving apparatus of the LED for the backlight of the conventional liquid crystal display apparatus further comprises feedback control units 14, 24 and 34 for controlling voltages feedbacked from the LEDs LED11 to LED13, LED21 to LED23, and LED31 to LED33 via the DC-DC converter units 12, 22 and 32, respectively, and Pulse Width Modulation (PWM) control signals providing unit 40 for providing a PWM control signal to the LED drivers 10, 20 and 30.
The PWM control signals serve to convert constant voltages, suitable for constant current driving of the LEDs LED11 to LED13, LED21 to LED23, and LED31 to LED33, into widths of waveforms, and control the converted waveforms.
The plurality of LEDs LED11 to LED13, LED21 to LED23, and LED31 to LED33 may be divided depending on the region of the backlight and then grouped, thereby forming a plurality of LED lamps G10, G20 and G30, respectively.
As described above, the conventional LED driving apparatus comprises the LED drivers 10, 20 and 30 and the feedback control units 14, 24 and 34 every LED lamps G10, G20 and G30 in order to independently control the luminance of the backlight region.
Accordingly, in order to construct the conventional LED driving apparatus, the LED drivers 10, 20 and 30 and the feedback control units 14, 24 and 34 must be respectively provided in proportion to the number of the divided backlight regions. Therefore, problems arise because the number of electronic elements necessary to construct the LED driving apparatus increases, and the cost for a driving circuit of the LED rises accordingly.
Furthermore, the size of the whole driving circuit of the LED increases. Also, the wiring structure of a Printed Circuit Board (PCB) in which the driving circuit of the LED is mounted becomes complicated.